Can – Could – Be able to

Bertie says, “I can’t speak!” Why? Because he wasn’t able to speak without pauses or without repeating the initial letters of words. He was a stammerer!

The swimming instructor says: “I have not had anyone who hasn't been able to do it within about five minutes.”

Examples

Can, can’t, cannot

We use can / can't

• to describe ability or lack of it.

My son can speak English fluently, but he can’t speak French.

 

• to describe what is allowed or not allowed.

You can visit Buckingham Palace but you can’t talk to the King.

 

• with a future meaning.

Sorry, but I can't come to the party next week.

 

• with verbs of perception: hear, see, taste, feel, smell.

What can you see?

I can smell gas!

Be able to

This has the same meaning as can.

We use be able to

• instead of can.

The King wasn’t able to speak easily, he stammered.

 

• when can is unsuitable. Because can has only present and past forms, we use be able to for other tenses, and infinitive form.

I haven't been able to finish my project.

We hope to be able to visit you next month.

Could vs Be able to

In an affirmative past simple sentence, we use “be able to” or “managed to” if we want to refer to something that someone succeeded in doing, something difficult on a specific occasion.

Although I was tired, I was able to finish my work.